2013

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One day, while running on a treadmill at the gym and listening to Celine Dion blast through the iPod of the woman walking on the treadmill next to me, I overheard a personal trainer approach the woman to give her some advice. “If you want to lose weight,” he said, “you should lift weights to increase your resting metabolic rate. Then you’ll burn more calories throughout the day.” A few minutes later, having suddenly noticed the absence of Celine’s voice, I spotted the woman in the corner of the gym, heeding the personal trainer’s advice and lifting weights, surely hoping for some better results.

In a society where people are constantly pressured to conform to specific ideals of what is considered attractive, it’s not surprising that strength training often takes on such a prominent role in the gym among personal trainers. After all, lifting weights may be the quickest way to improve your clients’ physical appearance and self-image. Strength training also has many functional benefits—improved muscular strength, posture and coordination; reversal of muscle-tissue losses that accompany aging; and increased bone mineral density, reducing the risk of osteoporosis. But does strength training affect resting metabolic rate (RMR)?

Each pound of fat-free weight (muscle plus everything else that is not fat) burns about 8 to 15 calories per day (Weinsier, Schutz and Bracco, 1992). Even as far back as 1971, Holliday (1971) calculated that RMR in children and adolescents was equal to 8 calories per pound of muscle per day. More recent research using body-imaging techniques to calculate organ surface area and energy cost has shown that each pound of fat-free body mass burns 6 to 7 calories per day (Bosy-Westphal et al., 2004; Gallagher et al., 1998), a negligible amount when one considers the 3,500-calorie deficit it takes to lose just 1 pound, and much lower than what is often publicized in the fitness industry and popular media.

In terms of oxygen consumption, RMR averages about 200 to 250 milliliters of oxygen per minute, or about 3.5 milliliters of oxygen per kilogram of body mass per minute. In clinical practice, RMR is commonly referred to as 1 MET (metabolic equivalent), with exercise recommendations and guidelines made in terms of multiples of METs. Because approximately 5 calories are burned for every 1 liter of oxygen consumed, the oxygen consumption of one MET equates to about 9 to 11 calories per pound of body mass per day. Thus, heavier people actually have a slightly higher RMR because they have more mass to support all day. If RMR was vastly different between people, we would not be able to define a MET the way we do, because there would be too much inter-individual variability. RMR is not as unique as a fingerprint. Not even close.

Although there is a positive relationship between fat-free weight (muscle mass) and RMR among animals and humans with large differences in body weight, RMR does not differ much between people, including between those who are fat and lean (Brooks et al., 2000) or of different aerobic fitness levels, and is independent of physical training status (Broeder et al., 1992a).

Can People Change RMR?

Perhaps the biggest myth in the fitness industry is the issue of resistance training increasing RMR by increasing muscle mass, which leads to greater weight loss. Although it is true that RMR is influenced by the amount of muscle your clients have, they would have to add a lot of muscle to significantly impact their RMR. It’s not like they can add 10 pounds of muscle (which is very difficult to do unless they train like bodybuilders for many months) and all of a sudden their RMR is double what is was before. As discussed earlier, research suggests there’s about a 10-calorie increase in metabolic rate for every pound of muscle. So, if a client’s RMR is 1,500 calories per day, he or she would need to add 15 pounds of muscle mass to increase it by 10%. Resistance training can make your clients look better because of the effect it has on their muscles, but it won’t really impact their resting metabolic rate all that much.

Humans’ RMR—the amount of energy we need to stay alive—is pretty stable, having been set by millions of years of evolution. Lifting dumbbells in a gym or doing burpees in the park is not going to change that. Some studies have shown an increase in RMR following weeks or months of exercise (Lemmer at el., 2001; Dolezal and Potteiger, 1998; Poehlman and Danforth 1991), but the magnitude of change is relatively small (about 30 to 140 calories per day) compared to what is needed for weight loss. Some of these studies have been done on seniors, whose RMR is more likely to be influenced by exercise training given the age-associated loss in muscle mass (sarcopenia) and the associated loss in muscles’ metabolic activity. It’s much easier to impact muscle mass, and thus RMR, in an older person than in a younger person. The majority of studies have shown that exercise does not increase RMR (Poehlman et al., 2002; Kraemer et al., 1999; Wilmore et al., 1998; Taaffe et al., 1995; Broeder et al., 1992b; Frey-Hewitt et al., 1990).

Post-workout Metabolism

Ever since the fitness industry found research showing that people burn calories after they work out while they recover from their workout, a whole new argument was born. Exercise stopped being about the exercise and became about what came after. “Do this workout,” trainers and gurus say, “because you’ll burn four times as many calories for up to 48 hours afterward.”

After some workouts, specifically those that are intense or long, you continue to use oxygen and burn calories because you must recover from the workout, and recovery is an aerobic, oxygen-using process. Body temperature must be lowered, muscle glycogen must be resynthesized, lactate must be transported from the muscles to the liver, acid-base balance must be restored, etc. This increased oxygen consumption following the workout is called EPOC (Excess Postexercise Oxygen Consumption).

Many studies have documented EPOC and compared it and its associated post-workout calorie burn between exercise of different intensities and durations (Tucker, Angadi and Gaesser, 2016; Laforgia et al., 1997; Treuth, Hunter and Williams, 1996), with high-intensity and longer-duration exercise causing a greater and longer boost to post-workout metabolism. However, the post-workout calorie burn caused by the EPOC is highly exaggerated by some health and fitness professionals. The increase in metabolism is transient, perhaps lasting a few hours, depending on how intense the workout was. The unbridled optimism regarding EPOC in weight loss is generally unfounded. Studies have shown that EPOC comprises only 6 to 15% of the net total oxygen cost of the exercise, and only when the exercise is very intense (Laforgia, Withers and Gore, 2006). Because unfit individuals recover more slowly than fit individuals, EPOC will be higher in unfit individuals. However, most unfit individuals simply can’t handle the intensity of exercise that is required to induce a high or prolonged EPOC.

The calories your clients burn when they exercise have a greater effect on body weight than the calories they burn afterward. It is the workout itself that creates the demand for change.

RMR and Weight Loss

RMR is often talked about in reference to weight loss. People lose weight only when they are in negative energy balance (i.e., caloric expenditure is greater than caloric intake). Research has shown that when people are in negative energy balance and losing weight, RMR actually decreases. This decrease occurs even when muscle mass is maintained by weight training (Geliebter et al. 1997). Exercise, especially weight training, can prevent the decline in RMR as people lose weight, but RMR certainly does not increase as they lose weight. Because no research has shown that RMR increases when people are in negative energy balance, it is not accurate to tell clients that weight training increases RMR that results in weight loss.

For fat loss, the effect of training is not about how much muscle your clients add to their bodies, but rather about how they enhance the metabolic profile of their muscles. This is because it is the change in composition of the metabolically active portions of muscles that accounts for any change in RMR. For example, endurance training enhances fat oxidation by increasing skeletal muscle mitochondrial content and cellular respiratory capacity. Weight training (or long, intense endurance training), provided it depletes muscle glycogen, helps repartition post-exercise food intake so ingested carbohydrates are used to replenish muscle glycogen rather than be stored as fat. Also, depleting muscles of glycogen (and then not consuming carbohydrates after the workout) threatens the muscles’ survival because carbohydrates are muscles’ preferred fuel. In response to this threat, muscles “learn” how to use fat more effectively. With the right training stimulus provided over many weeks and months, muscles become better fat-burning machines.

So, the next time a client asks about strength training and metabolism, explain to him or her that, while strength training is important for a variety of reasons, it will not cause weight loss by increasing RMR. With this new information, your clients may walk (or run) longer or faster on the treadmill to train their metabolically active muscles, and they may even wait until the drive home to listen to Celine Dion.

Weinsier, R.L., Schutz, Y. and Bracco, D. (1992). Reexamination of the relationship of resting metabolic rate to fat-free mass and to the metabolically active components of fat-free mass in humans. American Journal of Clinical Nutrition, 55, 790–794.

Wilmore, J.H. et al. (1998). Alterations in resting metabolic rate as a consequence of 20 wk of endurance training: The HERITAGE Family Study. American Journal of Clinical Nutrition, 68, 66–71.

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Author

Jason R. Karp, Ph.D.

Health and Fitness Expert

Jason Karp, Ph.D., is the 2011 IDEA Personal Trainer of the Year, 2014 recipient of the President’s Council on Fitness, Sports & Nutrition Community Leadership award, and creator of the REVO2LUTION RUNNING™ certification. He has authored more than 400 published articles in international running, coaching and fitness magazines, is the author of eight books, including 14-Minute Metabolic Workouts and Run Your Fat Off, and speaks at fitness conferences and coaching clinics around the world.

2013

Take the CEC Quiz as you read

In an effort to help you more efficiently earn continuing education credits while you explore
Certified, you can now take the quiz as you read. Get the latest, science-based information
while you earn 0.2 CECs.

Sign up to receive CERTIFIEDTM

Certified™ is a free online monthly publication from ACE designed to equip certified fitness professionals and health professionals alike with the knowledge they need to continue growing.